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Flexible Electrochromics Change Their Hue

Redox-active ion gel might one day enable low-cost, color-changing display devices made of plastic

by Mitch Jacoby
February 16, 2015 | A version of this story appeared in Volume 93, Issue 7

With the flick of a switch, “smart” windows and rearview mirrors lighten or darken as an applied voltage activates an electrochromic substance embedded in the glass. These devices reduce glare and can moderate the intensity of light and heat inside an automobile or building. But electrochromic devices tend to be expensive and rigid. A study reported in Chemistry of Materials suggests that a novel electrochromic gel may bypass those limitations, leading to new types of low-cost, flexible color-changing devices and electronic displays (2015, DOI: 10.1021/acs.chemmater.5b00026). The University of Minnesota’s Hong Chul Moon, Timothy P. Lodge, and C. Daniel Frisbie first treated an ion gel composed of a polystyrene-based block copolymer and an imidazolium compound with ferrocene and methyl viologen, which is redox active. The team then sandwiched the resulting electrochromic material between flexible transparent plastic conductors and showed that applying less than 1 V reversibly switched the device between colorless (oxidized) and colored (reduced) states. The researchers note that the device, which was made via simple solution processing, functioned stably in air for 24 hours.

This pair of photos shows a simple, flexible, polymer-based electrochromic device. Applying less than 1 volt reversibly activates (reduces) the electrchromic component, revealing a pattern of blue squares.
Credit: Chem. Mater.
Applying less than 1 V reversibly activates (darkens) the otherwise colorless electrochromic gel embedded in this flexible, plastic test device.


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